Method for forming a thin film using a gas

ABSTRACT

A starting gas feeding apparatus for forming a gaseous starting material from a liquid starting material and feeding the gaseous starting material into a reaction chamber of a CVD apparatus, comprises; a container that holds the liquid starting material, pressure reducing means for reducing the pressure inside the container, and heating means for heating the liquid starting material held in the container; the liquid starting material being boiled.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a chemical vapor depositionmethod and apparatus for forming various deposited films such as metalfilms, semiconductor films and insulating films used in memory devicessuch as semiconductor devices and optical magnetic disks or in flatpanel display devices. More particularly it relates to a chemical vapordeposition method and apparatus making use of a liquid startingmaterial.

[0003] 2. Related Background Art

[0004] Deposited films formed by chemical vapor deposition method (CVDmethod) using apparatus therefor (CVD apparatus) can be roughly groupedinto metal films, semiconductor films and insulating films.

[0005] Of these, in the case of the semiconductor films, a film formingmethod capable of obtaining uniform films with less faults are desired.As for the insulating films, uniform films are desired as a matter ofcourse and besides a film forming method that can achieve excellentcoating properties on step portion is desired. This is because mostinsulating films are used to insulate wirings from each other in anintegrated circuit (IC) or to protect its uneven surface.

[0006] In the case of the metal films, a film forming method that canachieve excellent uniformity and coating performance on step portion isalso desired as in the case of the insulating films. This is because themetal films are mostly used in wiring materials for ICs and in suchinstances the coating properties on step portion at the holes thereofare required so that upper and lower wirings can be connected viaopenings called contact holes or through holes.

[0007]FIG. 1 diagrammatically illustrates the prior art CVD apparatusused for such CVD method.

[0008] In FIG. 1, reference numeral 403 denotes a reaction chamberformed of quartz or the like, provided therein substrate holders 410that are disposed in plurality to support thereon a corresponding numberof substrates 409 on which films are to be formed. Reference numeral 408denotes an exhaust pipe, which is connected to a main pump 404 compriseof a mechanical booster pump and an auxiliary pump 405 comprised of arotary pump and from which the inside of the reaction chamber 403 areevacuated.

[0009] As for a gas feeding system, it is provided with a bomb (bubbler)402 having a bubbling mechanism that bubbles a liquid starting material,a gas pipe 406 through which carrier gas for the bubbling is fed, avalve 401, and a gas pipe 407 through which vaporized starting materialsare fed into the reaction chamber 403.

[0010] Such a conventional CVD apparatus can make full use of itsperformance so long as common film formation is carried out, but issometimes unsuitable for a CVD method that can excellently provide finestructure or form large area films as recently demanded. In other words,conventional apparatus have had some features that they are poor ingeneral-purpose properties, i.e., adaptability to any CVD methods. Thisproblem will be discussed below by giving an example.

[0011] Recently, as materials for the wiring of highly integratedsemiconductor devices called VLSI or ULSI, aluminum films formed not bysputtering but by CVD have attracted notice. In particular, in CVDmethods making use of an organic compound comprising an organoaluminumcompound, it is nowadays reported that conditions for deposition greatlydiffer between an insulator and a conductor and hence selectivedeposition can be made in which aluminum is deposited only on theconductor or a semiconductor. This selective deposition of aluminum isvery useful when fine integrated circuits are fabricated. In particular,in instances in which the ratio of depth to diameter (aspect ratio) of ahole is more than 1, the selective deposition can provide aluminumwiring that can not be realized by the sputtering which is a substitutetechnique. In the sputtering, disconnection occurs when the hole has alarge aspect ratio. The reason therefor will be explained below withreference to FIGS. 2A to 2C. In FIGS. 2A and 2B, reference numeral 201denotes a monocrystalline silicon substrate; 202, an insulating filmsuch as silicon dioxide film; and 203, a wiring material such asaluminum.

[0012]FIG. 2A illustrates how the wiring is formed when the hole has asmall aspect ratio, and FIG. 2B how the wiring is formed when the holehas a large aspect ratio of 1 or more.

[0013] In the sputtering, a hollow 204 or a void 205 is formed. On theother hand, in the selective deposition by CVD, the hole is completelyfilled with aluminum 303 as shown in FIG. 2C, and there is a very lowprobability of disconnection.

[0014] In FIG. 3, reference numeral 301 denotes a silicon substrate;302, an insulating film such as silicon dioxide film; 303, a metallicmaterial such as aluminum deposited by CVD; and 304, wiring of aluminumdeposited by sputtering or CVD.

[0015] Thus, in the case when the wiring of a fine semiconductor deviceis fabricated using the CVD apparatus shown in FIG. 1, a carrier gas CGSsuch as hydrogen, whose pressure is reduced by means of a reducing valve401, is fed to the bubbler 402. Most of material gases that enable theselective deposition of aluminum are liquid at room temperature, asexemplified by dimethylaluminum hydride (DMAH) and triisobutylaluminum(TIBA). For this reason, the bubbling, i.e. the step of generatingbubbles in the bubbler 402 is carried out, so that a mixed gas comprisedof the carrier gas and saturated vapor of organoaluminum compound suchas DMAH is fed into the reaction chamber. The mixed gas is thermallydecomposed on the heated semiconductor substrates 409, and aluminum isdeposited on the substrate as a result of its surface reaction with thesubstrates.

[0016] Unreacted gas in the reaction chamber 403 is exhausted outside bymeans of the main pump 404 and auxiliary pump 405.

[0017] However, a change in apparatus environment such that anexperimental CVD apparatus that has stably achieved the selectivedeposition is made up to a mass-production CVD apparatus has caused theproblem that the selectivity having been achieved so far is lost.

[0018] This results in an increase in faults not only in the case of themetal films but also in the case of the semiconductor films, and resultsin a lowering of step portion coating properties in the case of theinsulating films.

[0019] According to a finding made by the present inventors, the poorgeneral-purpose properties is caused by the following reasons, as willbe more detailed later, in the constitution of the conventional CVDapparatus.

[0020] First, the mixing ratio of the starting material liquid compoundand other gas can only be very poorly controlled.

[0021] Second, a temperature change in the vicinity of the bubblercauses a change in the mixing ratio of the compound.

[0022] Third, residual gases in the bubbler cause a change in the mixingratio of the compound.

SUMMARY OF THE INVENTION

[0023] An object of the present invention is to provide a chemical vapordeposition method and apparatus that can stably form deposited filmswith a good quality even if there are changes in environmentalconditions or changes in operational parameters.

[0024] Another object of the present invention is to provide a chemicalvapor deposition method and apparatus that has excellent operability andmass-productivity and promises the reduction of production cost ofvarious devices fabricated.

[0025] Still another object of the present invention is to provide achemical vapor deposition method and apparatus that can form depositedfilms that are uniform over a wide area, cause less unwanted faults andcan be formed in good step portion coating properties.

[0026] The present invention provides an apparatus for forming a gaseousstarting material from a liquid starting material and feeding thegaseous starting material into a reaction chamber of the CVD apparatuscomprising;

[0027] a container that holds the liquid starting material, pressurereducing means for reducing the pressure inside the container, andheating means for heating the liquid starting material held in thecontainer; the liquid starting material being boiled, and a CVD methodmaking use of the apparatus.

[0028] The present invention also provides an apparatus for feeding astarting gas into a reaction chamber with starting gas feeding means anddepositing a thin film on a substrate placed in the reaction chamber,wherein;

[0029] the starting gas feeding means comprises a heating apparatuscomprising a heating member having a plurality of through-holes throughwhich a starting gas is passed, temperature control means that controlsthe temperature of the heating member and a heater provided in thevicinity of the plurality of through-holes, controlled by thetemperature control means; the starting gas being fed into the reactionchamber through the through-holes, and a CVD method making use of theapparatus.

[0030] The present invention still also provides a CVD apparatuscomprising a container that holds a liquid starting material, a mixingchamber in which a gas of the starting material and other gas are mixed,a rectifier provided between the container and the mixing chamber; therectifier being provided with gas feeding means comprising a platemember provided with an opening having heating means.

[0031] The present invention further provides a CVD apparatus comprisinga head from which a starting gas is liberated toward a substrate placedin a reaction chamber; the head having a gas liberating surface at adistance of 10 mm or less from the surface of the substrate, and the gasliberating surface being detachably supported.

[0032] The present invention further provides a CVD apparatus forforming a deposited film comprised of the same material in a pluralityof film forming regions, wherein;

[0033] the plurality of film forming regions are provided between themwith means for turning a substrate, the substrate on which a film hasbeen formed in one of the film forming regions is turned by an anglewithin the range of larger than 0° to smaller than 360°, and thereafterthe substrate is placed in other film forming region to further form afilm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a diagrammatic illustration of a conventional CVDapparatus.

[0035]FIGS. 2A to 2C illustrate the states of deposited films formed.

[0036]FIG. 3 illustrates the state of a deposited film formed.

[0037]FIG. 4 is a graph to show the relationship between temperature andvapor pressure of a liquid starting material.

[0038]FIG. 5 is a diagrammatic illustration of a CVD apparatus accordingto Example 1 of the present invention.

[0039]FIG. 6 is a diagrammatic illustration of a conventional CVDapparatus.

[0040]FIG. 7 is a graph to show the relationship between starting gastemperature and feed efficiency.

[0041]FIG. 8 is a graph to show the relationship between starting gastemperature and deposition rate.

[0042]FIG. 9 is a graph to show temperature distribution of a startinggas at the in-plane position of a rectifying plate.

[0043]FIG. 10 is a diagrammatic illustration of a CVD apparatusaccording to Example 2 of the present invention.

[0044]FIG. 11 is a diagrammatic illustration of the structure of arectifying plate used in the present invention.

[0045]FIG. 12 is a diagrammatic illustration of the structure of anotherrectifying plate used in the present invention.

[0046]FIG. 13 is a diagrammatic illustration of a CVD apparatusaccording to Example 3 of the present invention.

[0047]FIG. 14 is a diagrammatic illustration of a CVD apparatusaccording to Example 4 of the present invention.

[0048]FIG. 15 is a diagrammatic illustration of a detachable head usedin the present invention, which is partially cut away to make thedescription easy to understand.

[0049]FIG. 16 is a diagrammatic top plan view of a CVD apparatusaccording to Example 5 of the present invention.

[0050]FIG. 17 is a view along the line X-X′ in FIG. 16.

[0051]FIG. 18 is a diagrammatic illustration of a modification ofExample 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Before specific description of the preferred embodiments of thepresent invention, technical items discovered to accomplish the presentinvention will be described below.

[0053] When, for example, the selective deposition is carried out by CVDusing DMAH and hydrogen, the following two reactions may proceed on thesurface of the semiconductor substrate having an insulating film withholes formed therein.

2Al(CH₃)₂H+H₂→2Al+4CH₄  (1)

2Al(CH₃)²H→2Al+2CH₄+C₂H₆  (2)

[0054] In this case, if the reaction proceeds as shown by scheme (1),the selectivity between the semiconductor surface and insulator surfacecan be ensured. If, however, simple thermal decomposition as shown byscheme (2) proceeds, no perfect selectivity between the semiconductorand insulator can be achieved on some occasions. This is caused by agreat influence the molar ratio of DMAH to hydrogen in the mixed gas hason the condition of deposition.

[0055] To avoid this problem, one may contemplate that hydrogen may bemixed in excess. The feeding of hydrogen in excess to a certain amountbrings about the problems that the deposition rate changes depending onthe diameter of the hole and that aluminum is buried in the shape of afacet as shown in FIG. 3 to achieve no flat burying. After all,appropriate control of the mixing ratio of DMAH to hydrogen isindispensable for a CVD method that can lead to a commercial success formanufacturers of semiconductors. An optimum mixing ratio will be studiedbelow.

[0056] The molar ratio in the case of the mixing of DMAH and hydrogendepends on the ratio of saturated vapor pressure of DMAH to partialpressure of hydrogen at the outlet of a bubbler. That is;

n _(DMAH) /n _(H2)=P_(DMAH) /P _(H2)(3)

[0057] wherein;

[0058] n_(DMAH) is a molar number of DMAH fed into a reaction chamber;

[0059] n_(H2) is a molar number of H2 fed into the reaction chamber;

[0060] P_(DMAH) is a partial pressure (saturated vapor pressure) of DMAHat the outlet of a bubbler; and

[0061] P_(H2) is a partial pressure of H₂ at the outlet of the bubbler.

[0062] The P_(DMAH) predominantly depends on the temperature, and isabout 1 to 2 Torr at best at room temperature. The P_(H2) can becontrolled by a pressure reducing valve, but its control precisiondepends on the precision of the reducing valve. When it is desired tocontrol the ratio of P_(DMAH) to P_(H2) to be several times, the P_(H2)comes to be ˜10 Torr, and hence the reducing valve must control thepressure in the order of several Torr. It, however, is very difficultfor any reducing valves on the present technical level to do so.

[0063] As shown in the above (3), the mixing ratio changes depending onthe P_(DMAH′) and the P_(DMAH′) which is merely a saturated vaporpressure, changes depending on temperature. FIG. 4 shows the temperaturedependence of DMAH on the saturated vapor pressure.

[0064] As shown therein, the P_(DMAH) exponentially changes with respectto temperature. On the other hand, since hydrogen is a gas at roomtemperature, the PH₂ does not exponentially change with changes oftemperature. In other words, the molar mixing ratio greatly changes withchanges of the temperature in the vicinity of the bubbler.

[0065] The hydrogen partial pressure P_(H2) at the the bubbler outletdoes not coincide with the hydrogen pressure at the bubbler inlet, andhas the relationship of:

P _(H2)(out)−P _(H2)(in)=c·ρ−h  (4)

[0066] wherein;

[0067] P_(H2) (out) is a hydrogen partial pressure at the outlet of thebubbler;

[0068] P_(H2) (in) is a hydrogen pressure at the inlet of the bubbler;

[0069] ρ is a specific gravity of an organometallic compound;

[0070] h is a distance from the tip of a bubbling nozzle to the liquidsurface in a bomb; and

[0071] c is a pressure calculating constant.

[0072] In this case, a variable that can be controlled by a regulator isonly the P_(H2)(in). Since, however, the value of h becomes smaller asthe apparatus is used, the P_(H2) (out) changes. As a result, in orderto keep the P_(H2) (out) constant, the P_(H2) (in) must be correctedaccording to the liquid remaining in the bubbler. However, this is atechnique accompanied by a great difficulty because of the structure ofthe device. As detailed above, the conventional CVD apparatus can not besaid to have a satisfactory starting gas controllability for theachievement of wide general-purpose properties and optimum depositionconditions.

[0073] According to the present invention, a starting material which isliquid at room temperature as exemplified by the organometallic compoundis weighed at the stage where it is liquid, to control the amount offeed. Thereafter, the starting material is formed into particles orevaporated using a vibrator, a Venturi means or the like, heated beforethe reaction and then fed into the reaction chamber in the form of agas. This constitution makes it possible to control the mixing ratio ofcarrier gas to other reaction gas at a high precision without influenceby variations in saturated vapor pressure of the starting material.

[0074] Thus, according to the present invention, it becomes possible toappropriately carry out all types of CVD methods.

[0075] In the cases other than metal films, e.g., in the case ofcompound semiconductors, the compositional ratio of elements can be wellcontrolled, and it becomes easy to form uniform semiconductor films orband gap controlled semiconductor films. In the case of insulatingfilms, it becomes easy to control x or y in Si_(x)O_(y) or Si_(x)N_(y),so that it becomes possible to form large-area films having a uniformdielectric constant.

[0076] In addition, it becomes possible to feed the starting material ina large quantity,-and hence it becomes easy to uniformly form films on alarge-area substrate or on a large number of substrates.

[0077] As the CVD starting material used in the present invention, amaterial that is liquid in a use environment of a CVD apparatus is used.More preferably it is a material that is liquid at room temperature,e.g, at 10 to 30° C. It may specifically include trimethylaluminum(TMA), triethylaluminum (TEA), triisobutylaluminum (TiBA),dimethylaluminum hydride (DMAH), diethylaluminum hydride (DEAH),monomethylaluminum hydride (MMAH), triethylindium (TEIn),trimethylindium (TMIn), trimethylgallium (TEGa), trimethylgallium(TMGa), dimethylzinc (DMZn), trichlorosilane (SiHCl₃), silicontetrachloride (SiCl₄), tetraethyl orthosilicate (TEOS),fluorotriethoxysilane (FOTES), POCl₃, BBr₃, Sn(CH₃)₄ and the like. Inparticular, organometallic compounds can be preferably used in the CVDmethod of the present invention because of their relatively low vaporpressure at room temperature and normal pressure and a difficulty intheir feeding in a large quantity. The reaction gas mixed with the abovesource material may include H₂, O₃, NH₃, NO, N₂ and the like. An inertgas such as Ar may optionally be used.

[0078] Of course, when compound films are formed or the type ofconductivity is controlled, a known doping gas as exemplified by PH₃,AsH₃, BF₃, B₂H₆, SiH₄ or Si₂H₆ may be used in combination.

[0079] The reaction chamber used in the present invention may be formedof an insulative reaction tube made of quartz or the like or a reactiontube made of a metal. The reaction tube used may be any of those capableof receiving therein at least one substrate on which a film is to beused.

[0080] An exhaust means may include a mechanical booster pump, a rotarypump, an oil-diffusion pump and a turbo-molecular pump, any of which canbe used alone or in appropriate combination.

[0081] The substrate is held in the reaction chamber by a substrateholding means in such a way that the deposition surface is set upwards,downwards, sideways, diagonally upwards or diagonally downwards.

[0082] The CVD apparatus constituted in this way is provided with agas-feeding means described later.

[0083] The deposited film formed by the present invention is a metalfilm including Al, In, Ga, Zn and Sn films, a compound semiconductorfilm including GaAs, GaAlAs, InP, ZnSe, Te, Si and SiGe films, an oxidefilm including SiO, SiON, SnO, InSnO, ZnO and ZnAlO films, or a nitridefilm including InN, AlN, SiN and BN films.

EXAMPLE 1

[0084]FIG. 5 best shows the features of the present invention. In FIG.5, reference numeral 101 denotes a liquid starting material such asDMAH; 102, a starting material container whose inner wall is formed ofan insulating material and which has a sufficient strength; 103 and 104,gas flow rate controllers such as mass flow controllers; 105 and 113,pressure gauges; 106 and 109, each an exhaust means set up incombination of a rotary pump and a mechanical booster pump; 110, apressure controller such as an automatic pressure controller; 108, athermostatic chamber having a heating mechanism, provided with a heatingelement over its whole partition walls; 111, a semiconductor substrateto be treated, such as a silicon wafer; 112, a heater for heating thesemiconductor substrate, provided to a substrate support; 114, anopposing electrode for discharging to bring a starting gas into plasmaexcitation; 115, a CVD reaction chamber; 116, a high-frequency powersource; 107 and 117, valves; and 118, a bomb for holding the liquidstarting material. In the container 102, no starting material is pouredat first, and the valve is kept shut. First, the inside of the container102 is well evacuated to a pressure of 1×10⁻⁵ Torr or less using theexhaust pump 106 and then the valve 107 is closed. Thereafter, the valve117 is opened, so that the liquid starting material is fed from thecontainer 118 into the container 102 via the valve 117. The system thatembraces the container 102 and the mass flow controller 103 is set inthe thermostatic chamber 108, and hence the liquid starting material canbe boiled at a given temperature in accordance with the reduced innerpressure whose environment is kept at any desired temperature. When, forexample, DMAH is used as the starting material, the temperature in thethermostatic chamber should be kept at 75° C. to 80° C. Particularlywhen the temperature is kept at 80° C. and the DMAH is used as thestarting material, substantially 100% of the inside of the container 102comes to be held by DMAH vapor, and gas pressure comes to be about 42Torr (see FIG. 4).

[0085] As for the pressure inside the reaction chamber 115, the reactionchamber 115 is evacuated using the exhaust pump 109 and its pressure iskept at 1 to 3 Torr, which is a proper deposition pressure, by means ofthe pressure control valve 110. The mass flow controller 103 may becomprised of a known device, and should be selected from those having amaximum controlled flow rate of about 200 sccm. As shown in FIG. 5, theDMAH and hydrogen gas are fed into the reaction chamber 115 at a flowrate of 200 sccm or less via the mass flow controller 103 and at a flowrate of 20 slm or less via the mass flow controller 104, respectively.When, for example, the DMAH gas and hydrogen gas are used as a mixed gasof starting gases and their partial pressure ratio is set by controllingthe flow rate using the mass flow controllers, the ratio of DMAH/H canbe arbitrarily set within the range of from 1/10 to 1/100. The totalflow rate of the mixed gas may preferably be controlled to be about 2 to20 slm.

[0086] The starting gases thus fed into the reaction chamber at a propermixing ratio come to the surface of the semiconductor substrate 111heated to 200 to 300° C. by means of the heater 112, and undergo thermaldecomposition there, so that the desired reaction product is depositedon the semiconductor substrate. This reaction is the reaction of thescheme (1) previously described, giving a good selectivity between theconductor and insulator, and thus the state of burying as shown in FIG.2C can be formed.

[0087] In the CVD utilizing the reaction between DMAH and hydrogen,non-selective growth can also be made by generating plasma across thesemiconductor substrate 111 and the electrode 114 by excitation using ahigh-frequency power source 116 (i.e., plasma CVD). By this plasma CVD,the metal deposited film as shown in FIG. 2C can be continuously formedin the same reaction chamber.

[0088] Each component part is provided with an interlock system as astabilizing system for improving safety and carrying out gooddeposition.

[0089] Stated specifically, the system is a monitor that detects theliquid level in the container 118. A means by which the deposition isstopped when the liquid therein becomes short and its level becomeslower than a certain level is attached to the container 118. It is alsopossible to put the deposition time in a memory.

[0090] The thermostatic chamber 108 is also provided with a means forpreventing overheat using a temperature sensor.

[0091] There is also provided a system by which the temperature andpressure inside the container are detected and the feeding of startinggas into the reaction chamber is stopped when the vapor pressure of thestarting material becomes lower than a given value, or the valve 107 isopened when it becomes more than another given value.

[0092] Other systems are also provided, e.g., a system for detectingabnormal discharge of plasma inside the reaction chamber and stoppingthe operation, and a system for detecting abnormal pressure inside thereaction chamber and stopping the operation.

[0093] The present invention can be applied not only to the CVDapparatus having the reaction chamber of sheet-by-sheet treatment asshown in FIG. 5 but also to a CVD apparatus having a reaction chamber ofmulti-sheet treatment according to a hot-wall system as shown in FIG. 1.

[0094] In the present invention, the exhaust systems 106 and 109 areseparately provided in the apparatus shown in FIG. 5. Alternatively, theend of the valve 107 may be inserted between the valve 110 and theexhaust system 109 so that the exhaust system can be omitted.

[0095] In the apparatus shown in FIG. 5, two-system gas lines areconnected to the container 102. Alternatively, the line having theexhaust system 106-107 may be omitted so that the inside of thecontainer 102 can be evacuated through the reaction chamber 115 by meansof the exhaust system 109.

[0096] As described above, as a method of feeding the liquid startingmaterial for the CVD apparatus, the starting material vapor comprised ofsubstantially 100% of the starting material is fed into the reactionchamber. Hence, it is weighed separately from other reaction gas andsent to the reaction chamber, where their mixing ratio can be maintainedat a proper value and in a high precision, and also can be stably fedinto the reaction chamber. Thus, it becomes possible to obtain a goodfilm quality and film configuration of the deposit of the reactionproduct.

[0097] Incidentally, in an instance in which the saturated vaporpressure of the liquid starting material is so low that the depositionrate is determined by the amount of feed of the starting material, it isknown to use the following apparatus as a method of improving feedefficiency of the starting material.

[0098]FIG. 6 is a diagrammatic illustration of a CVD apparatus used toform an aluminum-thin film, which is disclosed in Japanese PatentApplication Laid-open No. 2-38569.

[0099] A carrier gas 2002 is blown into a liquid starting material 2101through a valve 2201 and a mass flow controller 2202, and a mixed gas ofthe carrier gas and starting gas is fed into a reaction chamber 2006. Tothe inlet of the mixed-gas, a rectifier 2003 is fitted so that the gasescan be uniformly fed to the surface of a substrate. This rectifier makesit possible to increase the vapor pressure of the starting gas byheating a starting material tank 2001 by means of a heating mechanism2103 when the liquid source material 2101 has a small vapor pressure.This rectifier 2003 is comprised of several rectifying plates 2302 formaking gas flow uniform and a cylindrical frame 2301 to which therectifying plates are fixed, and the cylindrical frame 2301 is providedwith a built-in heater 2303. The heating mechanism 2103 of the startingmaterial tank is set at a temperature high enough to increase the vaporpressure and also low enough not to cause the starting gas to decompose,e.g., about 50° C. when an organometallic compound, triisobutylaluminum(TIBA), is used as the starting material. The heating mechanismbelonging to the rectifier 2003 is set at about 230° C., which is atemperature at which the aluminum thin film is most fittingly formed.

[0100] Then, a substrate 2005 such as a silicon wafer fitted to asubstrate holder 2004 is heated to about 400° C. by means of a heatingmechanism 2403, and as a result of thermal decomposition reaction of themixed gas fed thereto the aluminum thin film is formed on the substrate.

[0101] Reference numerals 2601, 2602 and 2603 denotes respectively avalve 2601 for introducing the mixed gas, a valve 2602 for evacuationand a gate valve 2603 from which the substrate is carried in or takenout.

[0102] However, a change in apparatus environment such that anexperimental CVD apparatus that has stably achieved the selectivedeposition is made up to a mass-production CVD apparatus has caused theproblem that the selectivity having been achieved so far is lost.

[0103] This results in an increase in faults not only in the case of themetal films but also in the case of the semiconductor films, and resultsin a lowering of step portion coating properties in the case of theinsulating films.

[0104] According to a finding made by the present inventors, these arecaused by an insufficient starting gas temperature control made by theheating system.

EXAMPLE 2

[0105] This Example is an improvement of the rectifier 2003 shown inFIG. 6, and has a structure that can form a gas flow having a uniformtemperature distribution.

[0106] In the prior art previously described, the heater 2303 externallyprovided was used in order to maintain the temperature of the rectifier2003 at, e.g., 80° C.

[0107]FIG. 7 is a graph to show the relationship between the temperatureinside the rectifier 2003 and the feed efficiency of the starting gasformed by evaporation. When DMAH is used as the liquid startingmaterial, the liquid starting material is evaporated by substantially100% if the temperature inside the rectifier is not higher than 100° C.and not lower than 40° C., and fed into the reaction chamber. If thetemperature is lower than 40° C., the material tends to be incompletelyevaporated to remain as liquid droplets in the rectifier. If thetemperature is higher than 100° C., about 0.1% of the starting gasundergoes decomposition inside the rectifier to cause deposition of Al.The Al deposited there may cause clogging of openings of a quartz plateto prohibit flow of the starting gas, resulting in a great decrease infeed efficiency for the rate of decomposition of as small as 0.1%.

[0108] What influence this fact has on the film formation is shown byFIG. 8. FIG. 8 shows the relationship between the temperature inside therectifier and the rate of deposition of an Al film.

[0109] In the CVD apparatus shown in FIG. 6, the flow rate of liquidDMAH and the flow rate of H₂ gas were measured to adjust them so as tobe 1:1 in molar ratio, and the rate of deposition of Al on amonocrystalline silicon wafer was measured. Results of the measurementare plotted with respect to the temperature of the rectifier.

[0110] In FIG. 8, the rate of deposition of Al is indicated as arelative value assuming as 1 the rate of deposition observed when thetemperature inside the rectifier is set at 80° C. As is clear from FIG.8, when the temperature is lower than 60° C., the vapor pressure of DMAHbecomes so excessively low that the reaction is retarded to cause anabrupt decrease in the rate of deposition. On the other hand, when thetemperature is higher than 100° C., the rate of deposition can not behigh because of a decrease in feed efficiency.

[0111] This means that precisely controlling the temperature inside therectifier is important for the process in which CVD is carried out afterthe liquid source material has been evaporated.

[0112] It has been also made clear that this temperature control must beprecisely made while the gas is being flowed.

[0113]FIG. 9 is a graph to show an in-plane temperature distribution ofa rectifying plate 2302 provided in the rectifier 2003.

[0114] White dots in FIG. 9 represent a temperature distribution of therectifying plate, observed when the gas is not flowed (an initialstate), and black spots represent a temperature distribution thereofobserved when the gas is being flowed (an operated state). As is clearfrom FIG. 9, since the gas flows without stagnating in the vicinities ofthe openings of the rectifying plate 2302, the temperature isconsiderably lower than the temperature initially set. That is, sincethe heat is taken away in the vicinities of the openings because ofsuccessive feeding of fresh gas, the temperature is dropped there. Suchan in-plane temperature distribution varies depending on the size of theopenings in the rectifying plate. In general, the larger the openingsare and therefore the larger the proportion of the openings to therectifying plate is, the larger the in-plane temperature distributionis.

[0115] Since the rectifying plates are mainly heated by heat conductionfrom its end to which a heating element is fixed, the temperaturedistribution occurs at the in-plane of each rectifying plate, and thisadversely affects the quality distribution of the film formed. Moreover,a great temperature change occurs in the rectifying plates particularlybefore and after the feeding of gas. At this time, the temperaturedistribution becomes more non-uniform between the rectifying plates. Thecylindrical frame having a built-in heater has a higher temperature thanthe rectifying plates and hence tends to cause thermal decomposition ofgas or deposition of Al. In some cases, depending on gas species, theoptimum temperature of the rectifying plates should be relatively low,e.g., about 80° C., in order to prevent the thermal decomposition ofgas. Such a low temperature, however, makes it more difficult to controlthe temperature.

[0116] In particular, even though a plurality of rectifying plates areprovided, the heating is controlled on the plurality of rectifyingplates as a whole, and hence the rectifying plate on the side near tothe substrate holder is affected by radiation of substrate heating. Thismakes it still more difficult to control the temperature.

[0117]FIG. 10 illustrates a second Example of the present invention.What is greatly different from the prior art shown in FIG. 6 is that arectifier 3003 is so set up as to carry out rectification while themixed gas is heated when the mixed gas containing the starting materialis fed into the reaction chamber 3006.

[0118] The rectifier 3003 is comprised of a heater 3307 as a heatingelement, a heating rectifying plate 3306 serving as a heating memberhaving a built-in temperature sensor, and an fixing frame 3308 of theheating rectifying plate. The gas is heated when passed through smallopenings arranged in the heating rectifying plate 3306, and then led tothe side of the reaction chamber 3006. The heating rectifying plateshould preferably be provided in plurality as shown in FIG. 10. Thefixing frame 3308 is so set up that it mechanically supports the heatingrectifying plate 3306, at the same time intercepts the gas from goingaround the fixing frame and also has a terminal through which the heater3307 of the heating rectifying plate 3306 is electrified.

[0119] In FIG. 10, reference numeral 4000 denotes a temperature controlsystem, which controls the quantity of current applied to the heater onthe basis of signals outputted from a temperature sensor provided to therectifying plate together with the heater 3307 as will be describedlayer.

[0120] In the case when the rectifying plate is provided in plurality,each heater and temperature sensor should be provided independently foreach rectifying plate so that its fine adjustment can be madeindependently.

[0121] This heating rectifying plate 3306 is has a structure as shown indetail in FIG. 11. That is, a thick film of C, Cu, Ni, Ag, Pd or ahigh-melting metal such as Mo, Ta or W is formed as the heater 3307 on aceramic substrate 3361 such as a boron nitride, alumina, zirconium,magnesia or cordierite substrate. To the both ends of the heater,terminal 3363 for power supply is provided, and is connected inside thefixing frame 3308 shown in FIG. 10. Reference numeral 3999 denotestemperature sensors provided arbitrarily in the area of the substrate.The ceramic substrate 3361 should be formed of boron nitride, having alarge thermal conductivity. The upper layer of the heater 3307 thusformed is covered with an insulating ceramic material for the purpose ofprotection. Through-holes are further arranged for the purpose of gasrectificaiton. In this example, the through-holes are made to have asize distribution so that the conductance at the outskirts where theflow velocity decreases can be increased.

[0122] Using this heating rectifying plate in plurality, plates havingthrough-hole size distributions different from each other-.can be usedso that the gas rectifying action can be improved.

[0123] A square or rectangular rectifying plate is shown in FIG. 11. Itis also possible to symmetrically arrange the through-holes in adisklike substrate. Of course, a variety of heater patterns can bedesigned so long as the vicinities of the through-holes can be heated.

[0124] Reference numeral 4001 denotes external terminals of thetemperature sensors, and 4002, external terminals of the heater. Theseare connected to the temperature control system 4000.

[0125] As another embodiment, as shown in FIG. 12, another ceramicsubstrate 3364 may be overlaid so that the heater is completely built into give a top-and-bottom symmetrical structure.

[0126] The present Example thus constituted can achieve a uniformin-plane temperature distribution as shown by x marks in FIG. 9previously given.

[0127] It also can achieve an improvement in temperature uniformity ofthe rectifying plate and also an improvement in the quality andthickness distribution of the film formed by CVD.

[0128] It still also can expand the scope of optimum conditions of gasheating temperature, flow rate and so forth, and at the same time canimprove reproducibility to give films with a good coverage.

[0129] In addition, the use of the heating rectifying plates in amultiple construction to make individual temperature control expands thescope of adaptation for liquid starting material gas species used, thestate of evaporation and so forth. It also brings about an increase infeed efficiency of the liquid starting material and an improvement infilm deposition rate.

[0130] These effects can be great particularly when liquid sourcematerials with a low saturated vapor pressure as in the organometalliccompounds are used.

EXAMPLE 3

[0131]FIG. 13 is a diagrammatical illustration of a gas feeding systemof the CVD apparatus according to this Example of the present invention.

[0132] Reference numeral 3006 denotes a reaction chamber, to which thesubstrate holder, the heater for heating substrates and so forth areprovided in the same manner as in the embodiments previously described.

[0133] This reaction chamber 3006 is provided thereto with a mixingchamber 3100 via a connecting pipe, and the mixing chamber 3100 isprovided beneath it with the same rectifier 3003 as in the Examplepreviously described. Further beneath the rectifier, a starting materialtank 3001 for holding a liquid starting material 3101, fitted with aheater 3103, is provided. The starting material tank is formed of quartzor a fluorine-treated insulating material.

[0134] On the side opposite to the reaction chamber side, the mixingchamber 3100 is connected to a carrier gas feeding means via aconnecting pipe.

[0135] This carrier gas feeding means contains a mass flow controller3202, a valve 3201 and a gas bomb 3203, and is further provided with aheater 3204.

[0136] This apparatus is operated as described below.

[0137] The liquid starting material 3101 kept in the source materialtank 3001 is heated with the heater 3103 to generate vapor therefrom.The heating temperature at this time is selected from temperatures thatcan give a vapor pressure as large as possible without little causingdecomposition of the starting material 3101. In the case of DMAH, thetemperature may preferably be 40° C. to 100° C. The pressure inside themixing chamber 3100 is controlled to be about 0.5 to 200 Torr accordingto the conductance of the connecting pipes. As for the starting materialtank 3001, its inside pressure is so made as to be 0.5 to 500 Torr byadjusting the size and density of the openings in the rectifying plateof the rectifier 3003. Stated specifically, the pressure inside the tank3001 is made equal to the saturated vapor pressure of the startingmaterial.

[0138] Then, Ar or N₂ as a carrier gas is fed from the gas bomb 3203into the mixing chamber at a temperature adjusted to 30 to 150° C., andpreferably 40 to 100° C., using the heater 3204.

[0139] Temperature of the starting gas generated by evaporation isprecisely controlled by means of the rectifier 3003 in the manner as inthe embodiment previously described.

[0140] Temperature of the gas in the rectifier 3003 is controlled to be40 to 100° C., and preferably 60 to 100° C.

[0141] Such temperature control of each heater is carried out by meansof the temperature control system 4000. In particular, controlling thetemperatures of the rectifier 3003 and heater 3103 makes it possible tohighly precisely control the rate of feed of the material gas makingreference to a condition equation (pV=nRT).

[0142] In the case when the selective deposition is carried out usingDMAH as the starting gas, not an inert gas but H₂ is used as the carriergas.

EXAMPLE 4

[0143] This Example is an embodiment in which the part (a head) throughwhich the mixed gas containing the starting gas is fed into the reactionchamber has been improved.

[0144] In Example 1 or 3, the starting gas is introduced from a lateralposition of the reaction chamber. In Example 2, the starting gas isintroduced from the rectifier toward the substrate in the reactionchamber.

[0145] Now, in the present Example, the starting gas is verticallyemitted to the substrate surface through means of a head assembly asshown in FIG. 14 so that the deposited film can be obtained from thestarting gas in a much higher yield.

[0146] As shown in FIG. 14, the head assembly 3501 is provided withthree rectifying plates 3306 made of quartz, in the same manner as inExamples 2 and 3. The openings in these plates are so made that they donot overlap each other, to set up communicating paths through which thegas introduced thereto mienders as shown by arrows AA in the drawing.

[0147] Beneath the rectifier, a dispersion head 3502 is detachablyprovided.

[0148] The dispersion head 3502 is comprised of a holder that isattached to or detached from the head assembly 3501, and a number ofplate members 3503.

[0149] In this head 3502, the distance between the gas blow-out surface3505 of the head and the deposition surface of the substrate 3005 shouldbe not more than 10 mm, preferably 1 to 10 mm, and more preferably 2 to5 mm so that the starting gas having been fed into the reaction chamber3006 can be utilized in a good efficiency to form a deposited film onthe substrate. The holder 3504 should be made to have a thickness Th of1 to 20 mm, and more preferably 3 to 17 mm.

[0150] The plate members 3503 and holder 3504 of the head 3502 is madeof stainless steel or silicon carbide.

[0151] According to the present Example, the starting gas is kept at aconstant temperature by means of the rectifier 3306, is uniformlydispersed by plates 3503 of the head which serve as a gas dispersionmeans, and reaches as shown by arrows AB the surface of the substrate3005 placed on the substrate holder 3004 having a heater.

[0152] Thus, the proportion of the starting material exhausted andrecovered through an exhaust system 3605 decreases, and hence the safetysystem that prevents gas from reacting in the exhaust system can be setup in a small scale.

[0153] Since the blow-out surface 3505 of the head assembly standsadjacent to the substrate holder 3004, it is possible that the head 3505receives the radiation of the heat for deposition, the temperature ofthe blow-out surface 3505 of the head reaches a deposition temperatureand a deposited film is formed there. Since, however, the head 3502 isprovided detachably in a known mechanical construction, its maintenancecan be made with ease. To give an example, when DMAH is used as thestarting material, a head made of silicon carbide is used as the head3502. Then, with repetition of deposition steps, Al is sometimesdeposited to the gas blow-out-surface in a thickness of 10 to 100 Å. Onthis occasion, the head 3502 can be readily detached to etch away thedeposited Al.

EXAMPLE 5

[0154] FIGS. 16 to 18 are diagrammatic illustrations of CVD apparatusaccording to Example 5 of the present invention.

[0155]FIG. 17 is a cross-sectional view along the line X-X′ in FIG. 16.In FIG. 17, reference numeral 3006 denotes a reaction chamber providedtherein with a substrate holder 5001 that holds a substrate 3005A in themanner reciprocatingly movable in the direction of an arrow DD andanother substrate holder 5002 that holds a substrate 3005B in the mannersimilarly movable in the direction of an arrow DD, which holders areopposingly provided interposing an intermediating turn table 5004between them.

[0156] Heads 5005 and 5105 are respectively provided above the holders5001 and 5002, which respectively comprise first gas head assemblies5007 and 5107 and second gas head assemblies 5006 and 5106.

[0157] For example, a material gas such as DMAH is fed into the firstgas head assemblies 5007 and 5107 through a pipe 5017 and a reaction gassuch as hydrogen is fed into the second gas head assemblies 5006 and5106 through a pipe 5016. In the case when the gases are fed into thereaction chamber in the form of a mixed gas, the head assemblies andpipes may be unified.

[0158] The present CVD apparatus is operated as described below.

[0159] First, the substrate having been subjected to film formation onthe holder 5001 while being reciprocated beneath the head 5005 issubsequently moved onto the turn table 5004. The turn table is turned by180° by means of a motor 5003. Of course, it may be turned by any angleexcept 360° or 0°, and preferably 30° to 330°, and more preferably 30°to 210°.

[0160] Next, the substrate having been moved onto the holder 5002 isagain subjected to film formation while being reciprocated similarly.These steps are carried out in the same reaction chamber 3006. Hence,with reference to FIG. 16, the right region A (5005A) of the substrateat the initial film formation corresponds to the left region B (5005B)at the subsequent film formation. Since the rate of film formation isdetermined by the flow rate of the starting gas in the case of DMAH orTiBA, the film formation should preferably be carried out independentlyin two or more film formation regions as in the present Example.

[0161] When the substrate is moved, there is a possibility that the filmthickness becomes uneven substantially in parallel to the direction ofmovement. Now, in the present Example, the substrate is turned by theangle except 0 and 360° within the deposition area by means of theintermediating means having the turn table, and then the subsequent filmformation is carried out. Hence, uniform films can be stably obtained.

[0162]FIG. 18 illustrates a modified embodiment of the present Example.Its film forming system is comprised of six heads 5005, 5105, 5205,5305, 5405 and 5505, three holders 5001, 5002 and 5003 and two turntables 5004 and 5014.

[0163] First, in a first film forming chamber DCA, the substrate issubjected to film formation on the holder 5001 while being reciprocatedbeneath the heads 5005 and 5105. Next, the substrate having been movedto a first intermediating chamber RCA is turned by 60° on the turn table5004, and then moved to a next, second film forming chamber DCB. Filmformation is also carried out here in the same manner as in the firstfilm forming chamber DCA. Thereafter, the substrate is further turned by60° in a second intermediating chamber RCB, and then moved in a thirdfilm forming chamber DCC, where the film formation is again carried out.

[0164] Each chamber can be independently evacuated by means of anexhaust system 3605 so as to be isolated from the atmosphere. Gatevalves (not shown) are also provided between chambers so that the filmforming atmosphere can be independently maintained for each chamber.

[0165] Of course, including the turn tables, all the heads and substrateholders may be provided in a common chamber as shown in FIG. 16.

[0166] In order to improve mass-productivity, however, the multi-chambersystem as shown in FIG. 18 should be taken and film formation is carriedout in such a way that at least one substrate is always present in eachfilm forming chamber.

[0167] Needless to say, the head in Example 4 may be employed in theheads 5005 and so on and, as the gas feeding system, the one used inExample 1 may be employed.

[0168] The present Example, in which the substrates are turned duringthe film formation, makes it possible to obtain uniform films withregularity and without uneveness.

[0169] Experiment 1

[0170] Using the apparatus of Example 1, deposition of Al was carriedout under typical conditions of a hydrogen flow rate of 500 sccm, a DMAHflow rate of 50 sccm, a reaction chamber pressure of 1.2 Torr and asubstrate heating temperature of 270° C. to form a metal film. As aresult, the metal film obtained was an aluminum thin film with anexcellent flatness and film quality.

[0171] Experiment 2

[0172] On the substrate having the Al film obtained in Experiment 1, asilicon oxide film was formed using the CVD apparatus having the sameconstitution as in Example 1.

[0173] A silicon oxide film of about 1 um thick was formed using TEOS asa starting material and ozone (O₃) as a reaction gas. The silicon oxidefilm obtained well covered the step portion and was flat.

[0174] Experiment 3

[0175] An aluminum thin film was formed using the apparatus of Example 2described above and using TIBA as a source material and Ar as a carriergas. As a result, the scope of conditions suited for film formationexpanded in respect of the flow rate of the starting gas and thetemperature of the gas feeding assembly, a good reproducibility wasachieved, and it was possible to well feed the starting gas.

[0176] An improvement was also seen in the film quality (surfaceroughness, specific resistivity, etc.) on the substrate. In particular,temperature was well controllable at the initial stage of the growth offilm, i.e., immediately after the feeding of gas and hence the Al filmwas well formed on the substrate having step portion.

[0177] In conventional gas rectifiers, a temperature distribution hascaused local deposition of Al films on the rectifier or abnormal growthof products. According to this experiment, however, it became possibleto better prevent such unauthorized deposition on the gas feedingassembly and to extend the maintenance period.

[0178] Experiment 4

[0179] Aluminum thin films were formed using the apparatus of Example 2and using dimethylaluminum hydride (DMAH) as a starting material and H₂as a carrier gas. Here, the temperature of the gas feeding assembly wasset at 80° C. and controlled for each of the plurality of heatingrectifying plates (three plates in this experiment). This was done toeliminate the influence of radiation heat coming from the substrateholder and to control the temperature low enough to preventdecomposition of the DMAH, as previously stated. Here, the substrate washeated at temperatures of 250° C. to 300° C. The individual control madeit possible to control the temperature of the rectifying plates at 100°C. or below even with respect to the DMAH decomposing at a relativelylow temperature, about 160° C., and contributed to improvements in therate of film deposition and the reproducibility of film quality.

[0180] Experiment 5

[0181] In the same apparatus as used in Experiment 4, the threerectifying plates were made to have a temperature gradient of from 10 to40° C. from the gas feed side toward the substrate side (e.g., the gasfeed side was set at 60° C., the center at 75° C. and the substrate sideat 90° C.). In this way the selective deposition of Al was carried out.In this experiment, it was possible to prevent occurrence of theundesirable condensation of saturated vapor of the starting materialinto a liquid, caused by local supercooling of the vapor when it flows,and it became possible to feed the starting material in a highefficiency. The rate of deposition of the film thus obtained was about 1μm/min.

[0182] In another example, the rectifying plates of the gas feedingassembly may be increased to 5 to 6 plates to provide a multiplestructure, where the temperature is controlled for each plate. Thismakes it possible to bring the gas into a good vaporized state when itis fed into the reaction chamber through the final heating rectifyingplate, even if the starting gas fed to the gas feeding assembly is in asupersaturated stated or contains liquid droplets. This brings about animprovement in feed efficiency of the starting material and animprovement in the film deposition rate.

[0183] In the above embodiments, the feeding of starting gas has beendescribed with reference to thermal CVD apparatus. The present inventioncan be very useful also in apparatus for other CVD such as plasma CVD,as a method of feeding starting materials comprised of organometalliccompounds.

What is claimed is:
 1. A starting gas feeding apparatus for forming agaseous starting material from a liquid starting material and feedingsaid gaseous starting material into a reaction chamber of a CVDapparatus, comprising; a container that holds said liquid startingmaterial, pressure reducing means for reducing the pressure inside saidcontainer, and heating means for heating said liquid starting materialheld in said container; said liquid starting material being boiled.
 2. ACVD apparatus comprising a reaction chamber, exhaust means that evacuatethe inside of said reaction chamber, substrate supporting means thatsupports substrate in said reaction chamber, and a gas feeding meansthat feeds a gaseous starting material into said reaction chamber,wherein; said gas feeding means comprises a container that holds saidliquid starting material, pressure reducing means that reduces thepressure inside said container, and heating means that heats saidstarting material held in said container; said liquid starting materialbeing boiled to form said gaseous starting material.
 3. The CVDapparatus according to claim 2, wherein said starting material comprisesan organometallic compound.
 4. A CVD method for forming a deposited filmon the substrate, making use of the apparatus according to claim
 2. 5.The CVD method according to claim 4, wherein an alkylaluminum hydride isused as the starting material, which is reacted with hydrogen to form ametal film mainly composed of aluminum, on the surface of a conductor orsemiconductor of the substrate.
 6. A CVD apparatus for feeding astarting gas into a reaction chamber with starting gas feeding means anddepositing a thin film on a substrate placed in said reaction chamber,wherein; said starting gas feeding means comprises a heating apparatuscomprising a heating member having a plurality of through-holes throughwhich a starting gas is passed, temperature control means that controlsthe temperature of said heating member and a heater provided in thevicinity of said plurality of through-holes, controlled by saidtemperature control means; said starting gas being fed into saidreaction chamber through said through-holes.
 7. The CVD apparatusaccording to claim 6, wherein said starting gas comprises anorganometallic compound.
 8. A CVD method for forming a deposited film onthe substrate, making use of the apparatus according to claim
 6. 9. TheCVD method according to claim 8, wherein an alkylaluminum hydride isused as the starting gas, which is reacted with hydrogen to form a metalfilm mainly composed of aluminum, on the surface of a conductor orsemiconductor of the substrate.
 10. A CVD apparatus comprising acontainer that holds a liquid starting material, a mixing chamber inwhich a gas of said starting material and other gas are mixed, arectifier provided between said container and said mixing chamber; saidrectifier being provided with a gas feeding means comprising a platemember provided with an opening having heating means.
 11. A CVDapparatus comprising a head from which a starting gas is liberatedtoward a substrate placed in a reaction chamber; said head having a gasliberating surface at a distance of 10 mm or less from the surface ofsaid substrate, and said gas liberating surface being detachablysupported.
 12. A CVD apparatus for forming a deposited film comprised ofthe same material in a plurality of film forming regions, wherein; saidplurality of film forming regions are provided between them with meansfor turning a substrate, the substrate on which a film has been formedin one of said film forming regions is turned by an angle within therange of larger than 0° to smaller than 360°, and thereafter saidsubstrate is placed in other film forming region to further form a film.